El Nino 2009-2010: What does it mean for southern Wisconsin? (updated Apr. 7)

Updated charts to compare the forecast to what was observed in June 2009- March 2010

An El Nino Advisory has been posted for the El Nino conditions that developed this summer and should persist into this winter season. This means that ocean waters along the Equator in the tropical Pacific Ocean are warmer than normal. The last two winters have featured the opposite, with colder than normal waters in that area and La Nina conditions.

What does this all mean for southern Wisconsin? Let's take a look at history and see if we can find some answers.

Looking back through 1950, we looked for La Nina conditions one winter that were followed the next winter by El Nino conditions. Six years were identified: 1951, 1957, 1963, 1965, 1972, and 1976. We then looked at the average temperatures, precipitation, and snowfall at Madison and Milwaukee in those six years and compared it to the normal values. The dataset is rather small, but the results did show some signals for the period of June through March.

1) Temperatures were colder than normal, especially in December

2) It tended to be drier than normal, especially in the summer and again around November

3) There was less snow than normal, especially in January and February

The following are graphics that compare the Madison and Milwaukee 30 year normal values to the average of the observed conditions during those 6 years when La Nina winters were followed by El Nino winters the next season. The time period covered starts during the summer between those winters and the El Nino winter, which is what we expect to happen for the 2009-2010 winter season.